I am creating a non-fiction ebook in ePub format in Sigil. I imagine it must certainly be possible to create forward links from the Table of Contents and backward links from Index entries - but I can't discover how to do it! Advice welcome.

Thanks. Had found the TOC editor, but your advice led me to the HTML I needed for Contents - <h1 title="Alternate text">Normal text</h1> . Index entries linking back to specific paragraphs in the text a different problem though.

Thanks. Had found the TOC editor, but your advice led me to the HTML I needed for Contents - <h1 title="Alternate text">Normal text</h1> . Index entries linking back to specific paragraphs in the text a different problem though.

Read the HTML specs about Anchors <a and using hash marks

As GeoffC said: some readers incorporate a back button.
Mine has one, but only if I used the "Catalog" button to get there (Catalog is the TOC that comes from the NCX file,which is whot the TOC editor shows you).
Inline-(HTML) TOC, put all the linkage burden on the Author.

Well you can, there can be multiple return points in a list and you click the one that returns you to the correct point. We have this feature in our wiki by the way where multiple links can refer to the same text, and you have a list of returns numbered the same as the references.

I meant that you can't if the footnote number is a return link (what I assumed is what Word does). There is only a footnote number, so it can be a link to a single place. Of course, if the return link is something added to the footnote, you can have as many as you like, and I've done that several times